Angelic Accord rewards your constant life gain with 4/4 angel threats that can present an alternate win condition
Well, that and a lot of card selection
Indoraptor, the Perfect Hybrid The mana cost on Indoraptor, the Perfect Hybrid makes it a bit weird to fit into a Cube, but its reasonable to just slot it in as a Gruul or Rakdos card, and some Cubes just have space for gold oddballs
Both of these cards are capable of doubling your mutate spells
One of Magic's best demons, Bloodletter of Aclazotz does a lot for your life drain shenanigans in any format
Ideally, you'd have fewer than four cards in your hand to gain some card advantage, but not so many fewer that you don't get a decent power boost for your creatures